1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having a Cu wire made of a metallic material mainly composed of Cu (copper).
2. Description of Related Art
In a highly integrated semiconductor device, Cu having higher conductivity than Al (aluminum) may be employed as the material for a wire. A wire (a Cu wire) employing Cu as the material therefor is embedded in a fine groove formed in an insulating layer on a semiconductor substrate by a damascene process, since it is difficult to finely pattern Cu by dry etching.
In general, SiO2 (silicon oxide) is employed as the material for the insulating layer. However, Cu has high diffusibility into SiO2. When the inner surface of the groove formed in the insulating layer made of SiO2 and the Cu wire are directly in contact with each other, therefore, Cu diffuses into the insulating layer, to reduce the dielectric voltage of the insulating layer. Therefore, a barrier film for preventing Cu from diffusing into the insulating layer must be provided between the insulating layer and the Cu wire.
A self-formation process employing an alloy material (hereinafter simply referred to as a “CuMn alloy”) containing Cu and Mn (manganese) is known as a technique of forming the barrier film. In the self-formation process, an alloy film made of the CuMn alloy is formed on the surface of the insulating layer including the inner surface of the groove by sputtering. Then, a Cu layer made of a metallic material mainly composed of Cu is stacked on the alloy film by plating. Thereafter heat treatment is performed, whereby Mn contained in the alloy film is bonded to Si (silicon) and O (oxygen) contained in the insulating layer, and a barrier film made of MnxSiyOz (x, y and z: numbers greater than zero. MnxSiyOz is hereinafter simply referred to as “MnSiO”) is formed on the inner surface of the groove.
After the formation of the barrier film, the surface of the Cu layer is polished by CMP (Chemical Mechanical Polishing) until the same is flush with the surface of the insulating layer out of the groove. Thus, a Cu wire embedded in the groove through the barrier film is obtained.
Excess Mn not contributing to the formation of the barrier film (bonding to Si and O) diffuses into the Cu layer. If the quantity of Mn diffusing into the Cu layer is large, Mn remains in the Cu wire, to increase the resistance of the Cu wire. While the specific resistance of pure Cu is about 1.9 to 2.0 μΩ·cm, the specific resistance of Cu containing Mn by 1% (at. %) in atomicity is about 5 to 6 μΩ·cm. In a fine Cu wire having a width of 60 to 70 nm, slight increase in specific resistance leads to remarkable increase in wire resistance.
In order to reduce the quantity of Mn remaining in the Cu wire, the alloy film made of the CuMn alloy may be set to the minimum thickness necessary for forming the barrier film.
When the alloy film is formed by sputtering, however, the CuMn alloy is harder to bond to the side surfaces of the groove as compared with the bottom surface thereof. If the alloy film is formed to have the minimum thickness necessary for forming the barrier film on the bottom surface of the groove, therefore, portions of the alloy film formed on the side surfaces of the groove are excessively reduced in thickness. Adhesiveness of the CuMn alloy to SiO2 is not high, and hence the adhesiveness between the alloy film and the side surfaces of the groove may be reduced to result in separation of the alloy film from the side surfaces of the groove if the alloy film is excessively reduced in thickness on the side surfaces of the groove. When the alloy film separates from the side surfaces of the groove, the barrier film made of MnSiO cannot be excellently formed on the separating portions.
Therefore, the alloy film is formed with a thickness larger than the minimum thickness necessary for forming the barrier film, in order to ensure the adhesiveness of the alloy film to the inner surface of the groove and prevent separation of the alloy film from the side surfaces of the groove. The adhesiveness of the CuMn alloy to SiO2 is reduced as the Mn concentration therein is decreased, and hence a CuMn alloy having a relatively high Mn concentration is employed as the material for the alloy film. Therefore, the alloy film excessively contains Mn.